Hydrocarbons, such as crude oil, heavy oil, vacuum residue, solvent-deasphalted oil, solvent-deasphalted residue, cracked oil, shale oil, tar sand oil and natural asphalt, contain various non-metallic and metallic impurities, which may adversely affect various processes for treating hydrocarbon fractions thereof. Most of the non-metallic impurities are compounds of nitrogen, sulfur and oxygen, and these are combined with high molecular weight asphaltene compounds and colloidally dispersed in the hydrocarbons. The metallic impurities include compounds of nickel, vanadium, iron, calcium, magnesium, copper, lead and zinc, especially those of nickel and vanadium. These metals are present in the hydrocarbon oils in the form of organo-metallic compounds, such as porphyrine, chelates and naphthenates, or in a form in which such organo-metallic compounds are combined with asphaltenes. Furthermore, the metals may also be present in the hydrocarbons as suspended metal oxides or sulfides, or as water soluble salts. These impurities possibly cause air-pollution problems when hydrocarbons containing the same are used as a fuel, and adversely affect reforming, cracking or other catalytic processes of hydrocarbons, by poisoning the catalysts used in such processes.
Removal of such impurities from hydrocarbons containing the same is an essential requirement in the art, and various processes have heretofore been proposed for removing sulfur and metals from hydrocarbons. The most simple measure to avoid metallic impurities is the use of lower boiling fractions in catalytic processes, based on the established knowledge that the metallic impurities are normally concentrated in higher boiling fractions. Alternatively, based on the knowledge that hydrocarbons in which the metallic impurities have been concentrated are sparingly soluble in certain low boiling solvents, processes are also known in which the hydrocarbons are subjected to a solvent extraction step for a substantial reduction in the metallic impurities. However, each of the processes provides a considerable yield of a residue in which the metallic impurities have been concentrated. In addition to the content of metals, contents of sulfur, nitrogen and asphaltene have also been concentrated in the residue. Such a residue has no valuable use except as the lowest form of fuel oil, which will inevitably invite air-pollution problems. Accordingly, none of the above-mentioned known processes is satisfactory from the viewpoint of full utilization of oils and energy or economics.
For the hydrodemetallization of hydrocarbons, processes have also been proposed in which the hydrocarbons are treated with hydrogen at high temperatures and pressures in the presence of certain catalysts. Such processes have been widely used for the removal of metals from hydrocarbons. Such processes are, however, disadvantageous in that a considerable proportion of the hydrogen used is consumed in side reactions, such as hydrogenating cracking, and in that the catalysts are expensive and the activity of the catalysts is considerably reduced by deposition of the metals thereon (that is, the allowable level of the amount of metals deposited on the catalysts is low). Accordingly, it is desired to develop an inexpensive catalyst having a high activity and a high selectivity for the desired demetallizing reactions. One of the known improved catalysts is disclosed in Japanese Laid-open patent specification No. 49(1974) - 122,501(Japanese patent application No. 48(1973) - 36,985) for "PROCESS FOR THE REMOVAL OF VANADIUM AND NICKEL FROM HYDROCARBONS", wherein the catalyst is based on red mud. According to the above-mentioned laid-open specification, red mud is used as a catalyst without being subjected to any particular treatment. Thus, the requirement for low cost is satisfied. However, the activity and selectivity of the catalyst for the demetallization are still unsatisfactory. In fact, according to the detailed description and data given in the laid-open specification it will be noted that the hydrogenating cracking reactions occur to a great extent together with the desired demetallizing reactions. That is, the % yield of either C.sub.1 -C.sub.5 or C.sub.5 -- 300.degree. C. fraction is as high as at least several or ten times that obtainable with the conventional desulfurizing catalyst for achieving the same % removal of metals. Furthermore, it is obviously expected from this result that desulfurizing and deasphalting reactions also occur in the process of the abovementioned laid-open specification, and thus it is believed that the process of the laid-open specification suffers from a considerably high consumption of chemical hydrogen and a fairly vigorous generation of the heat of reaction. Moreover, it should be also noted that the by-production of a higher yield of low boiling oils is accompanied by a larger amount of recirculated purging hydrogen. Thus, in view of the increased amount of hydrogen consumed and the complicated reaction apparatus, both resulting from the low selectivity of the catalyst for the demetallizing reactions, the process of the above-mentioned laid-open specification is not advantageous not only from the viewpoint of technology but also from the viewpoint of economy, although the catalyst used is itself inexpensive. Furthermore, while no reference is made in the laid-open specification with respect to the manner of contacting the reactants with the catalyst, the catalyst is necessarily used in the state of a slurry because the untreated red mud is fine enough to pass through a screen of 300 mesh. Therefore, the reaction apparatus and conditions of the process of the laid-open specification are limited and unflexible.